The present invention relates to apparatus for measuring electromagnetic radiation, and particularly to apparatus which can be used in the measurement of the degree of risk from electromagnetic radiation, the so-called radiation hazard.
The continuing increase in the number of both civil and military applications of electromagnetic energy at radio frequency means that an ever increasing number of people, especially completely unskilled people, now come into contact with sources of radiation. However, it is known that high intensity electromagnetic radiation can produce harmful biological effects, and since there is no unanimous agreement on the threshold value at which such radiation becomes hazardous the need for measuring apparatus which permits the evaluation in a precise and rapid manner of the intensity of such radiation will be appreciated. Such apparatus can be used both for identifing dangerous environments or regions and for checking on the efficiency of protective screening apparatus.
Various types of apparatus for measuring electromagnetic radiation are currently available commercially. Mostly, such apparatus operates by measuring the power density as is confirmed by the article "quantifing hazardous electromagnetic fields: scientific basis and practical considerations" by P. F. Wacker and R. R. Bowman, appearing in IEEE Transactions on Microwave Theory and Techniques, Volume MTT-19, No. 2, February 1971. Such apparatus, whilst giving results which are satisfactory with plane electromagnetic waves, gives grossly inacurate results when the measurement is made in close proximity to the source of radiation, that is in near-field conditions. This disadvantage is particularly serious since the radiation hazard is very much greater in proximity to the source.
Another serious disadvantage of such apparatus lies in the fact that it is necessary, in general, for the operator to be present during the measurement. This means that the operator is exposed to the radiation being measured and, moreover, the operator's body has a perturbing influence on the form of the electromagnetic field, contributing to distortion of the measurement.